[luatex] portable fmt between 32-bit/64-bit machines

[Michal Vlasák]

On Tue Feb 8, 2022 at 1:58 AM CET, Michal Vlasák wrote:
> I posted a few more details on github:
>
> https://github.com/latex3/latex2e/issues/775#issuecomment-1032099002

An update to the proposed patch (more apparent error checking, correct
for both LuaJIT/5.1 and 5.3). And hopefully a solution to the
portability issue at hand (at least for some architectures).

https://github.com/latex3/latex2e/issues/775#issuecomment-1032138520

Hans, Luigi, what do you think?

Of course there is a runtime cost, though negligible and it brings space
savings, which is a trade off the Lua guys have already made in 5.4.

I also think that the byte swapping for big/little endian could be done.
If the saved format is little endian there should be no cost for most
architectures (unlike the dump sharing on TeX side).

Kind of related:

https://mailman.ntg.nl/pipermail/dev-luatex/2021-July/006501.html

Michal